1. Field of the Invention
The present invention relates to axle/suspension systems, and in particular to lift-type axle/suspension systems of heavy-duty commercial vehicles. More particularly, the invention relates to an apparatus that controls the transfer of air between one or more air springs which lift the axle and ride air springs of the axle/suspension system.
2. Background Art
Many commercial vehicles currently utilize suspension assemblies that can retract and thereby raise the axle of the axle/suspension system off the ground. Such suspension assemblies conventionally are known in the industry as lift axle suspensions. Lift axle/suspension systems usually are paired or grouped with non-lift axle/suspension systems on a vehicle, the latter of which are commonly referred to as primary axle/suspensions systems. The majority of lift axle/suspension systems utilize one or more pneumatic air springs to raise or retract the axle/suspension system. Pneumatic air springs of that type typically are referred to as lift air springs and generally can be placed in a variety of locations relative to the axle/suspension system to accomplish the lifting function. Another set, usually a pair, of pneumatic air springs is utilized to lower or extend the axle/suspension system for assisting in supporting the vehicle load, and typically are referred to as ride air springs.
Lift axle/suspension systems usually are retracted or raised when the vehicle load is less than the load capacity of the primary or non-lift axle/suspension systems, or when greater vehicle maneuverability is required. A number of different types of pneumatic or electro-pneumatic systems can be employed to operate lift axle/suspension systems, depending on the application and customer requirements. The present invention can be utilized with most types of such operating systems, and also generally can be used regardless of the location of the one or more lift air springs. Most such systems operate by simultaneously but independently supplying pressurized or compressed air to the lift air springs and exhausting air pressure from the ride air springs when it is desired to retract or raise the axle/suspension system. Conversely, when it is desired to lower the axle/suspension system to support a load, air pressure is supplied to the ride air springs and exhausted from the lift air springs.
Although such prior art operating systems accomplish their goal of raising and lowering the axle/suspension system, a number of drawbacks are inherent in those systems. More particularly, such prior art operating systems often suffer from low overall system air pressure and lack the ability to rapidly deliver pressurized air to the relatively large ride air springs. For example, every time the axle/suspension system is raised or lowered, air pressure from a set of air springs, either the ride air springs or the lift air springs, respectively, is exhausted to the atmosphere. This exhaustion or complete loss of a certain amount of compressed air significantly adds to the total air consumption of the vehicle and increases the demands on the vehicle compressor which supplies such pressurized air. If the lift axle/suspension systems, together with other air-consuming vehicle devices such as the brakes, are operated repeatedly over a short period of time, demand for pressurized air can exceed the compressor capacity, making it unlikely or impossible for all of the devices to operate at full capacity. More importantly, insufficient air pressure in those devices can cause premature failure of axle/suspension system components such as axles, beams, and even vehicle frame components, the primary cause of which is low air pressure in the axle/suspension system ride air springs.
Moreover, the ride air springs themselves can be damaged due to such low pressure. More particularly, in prior art air spring operating systems, as air pressure is exhausted from the lift air springs, those springs contract and gravity pulls the axle/suspension system in a downward direction. This downward movement of the axle/suspension system also extends the ride air springs. If the ride air spring operating system fails to simultaneously deliver pressurized air to the ride air springs fast enough when the axle/suspension system is lowering, the ride air springs can become extended before they are sufficiently filled with pressurized air. This lack of air pressure results in the ride air spring failing to be adequately distended, thereby causing its elastomeric flexible member to buckle or fold which can result in undesirable damage to the air spring.
The control apparatus of the present invention greatly reduces or eliminates the above-described problems by integrating control of the lift and ride air springs rather than allowing them to operate completely independent of one another. It is understood that the majority of lift axle/suspension systems typically use only a single lift air spring and a pair of ride air springs thereby requiring the use of only one control apparatus of the present invention. The illustrative system described below in detail in the description of the preferred embodiment has a pair of lift air springs and a pair of ride air springs. In such lift axle/suspension systems that utilize two lift air springs with the two ride air springs, one or two control apparatus can be utilized as desired without affecting the overall concept of the present invention.
More specifically, to prevent the above-described ride air spring buckling caused by low air pressure, the present invention utilizes an air pressure transfer line which extends between and preferably is pneumatically connected to a tee located in an exhaust port of the valve that controls operation of the lift air spring and the conduit that connects each of the ride air springs to their control valve. A one-way check valve located in the air pressure transfer line allows pressurized air to flow only in the direction from the lift air spring to the ride air springs. A choke valve installed in the exhaust port of the tee allows pressurized air to be fully exhausted from the lift air spring, but at a restricted rate.
As is well known in the suspension industry, pressurized air typically is supplied from the vehicle compressed air reservoir to the ride air springs via a height control valve and a dump valve, and to the lift air spring via a regulator and a valve. The present invention control apparatus as described immediately above supplies additional pressurized air from the lift air spring to the ride air springs when the axle/suspension system is being lowered, thus providing adequate air pressure to each ride air spring to rapidly inflate the flexible member during the lowering process, thus minimizing buckling and folding and potential damage to the ride air spring and other components of the vehicle. The present invention also minimizes the possibility that the vehicle compressor will lack capacity to supply air to all of the vehicle components requiring such air to operate. Specifically, because of the additional or recycled pressurized air flowing into the ride air springs from the lift air spring, less overall pressurized air is required from the vehicle air compressor to inflate the ride air springs to the proper pressure, since not all of the air in the lift air spring is being exhausted to the atmosphere every time the axle/suspension system is lowered. Since more air is conserved, the possibility of low vehicle air pressure, and its potential negative impact on components of the lift axle/suspension system, is minimized or eliminated.